Process for the adjustment of a brake power booster travel sensor

ABSTRACT

A process for adjusting the travel sensor for a brake power booster movable wall is disclosed to compensate for tolerance variations, in which a fixed stop is installed to engage the output member upon applying a predetermined input force to shift the movable wall to a test location. The distance to the test location of the movable wall from a booster housing reference surface is measured with a measuring instrument installed temporarily in the booster housing opening normally receiving the travel sensor. The tips of the travel sensor is positioned at the test location with the travel sensor in the corresponding signal condition either by using an appropriately dimensioned replaceable tip or sensor holder, or by use of an adjustable length sensor holder.

BACKGROUND OF THE INVENTION

The invention is related to a process for the adjustment of a travelsensor for a vacuum brake booster for automotive vehicle brake systemshaving an anti-locking device. The electrical travel sensor monitors theposition of a movable wall which furnishes the boosting power of thevacuum brake power booster. In particular, the invention relates to aprocess for the adjustment of the desired axial distance between anactuating element of the travel sensor and the movable wall.

It is, for example, known from the German patent application publishedwithout examination, No. 3,731,603, corresponding to U.S. Pat. No.4,826,255, to sense the position of the movable wall in order tosafeguard the regular functioning of brake systems with anti-lockingdevice which work as "open" systems. U.S. Pat. No. 5,141,295 filed onDec. 19, 1989 assigned to the assignee of this application alsodescribes such movable wall sensor for a brake power booster for thispurpose.

In these arrangements, a rotary hydraulic pump is provided, which, inone control mode, aspirates hydraulic fluid out of an unpressurizedsupply tank, and with the wheel valves in the closed condition, deliversthe same into the master brake cylinder in order to properly positionthe brake pedal. For this purpose, a travel sensor, for example, atravel-controlled electric switch, is envisaged which supplies anelectrical signal depending on the position of the movable wall to anelectronic control system which controls the pumping rate of the pump.

The vacuum brake power booster, in particular its housing, is subject tosizable working tolerances which have a negative effect on thefunctioning of the travel sensor and, in an extreme case, may even leadto the total failure of the brake system.

It is, therefore, the object of the invention to provide a process forthe adjustment of the exact position of the electrical travel sensor inrespect of the movable wall of a vacuum brake power booster, whichaffords a virtual elimination of the influence of its working toleranceson the functioning of the travel sensor.

SUMMARY OF THE INVENTION

According to the invention, this object is achieved by the followingprocess steps:

a) installing a stop in the booster housing for the output member drivenby the booster movable wall, the stop having a defined length;

b) applying a vacuum to the vacuum chamber in the booster housing;

c) actuating the vacuum brake power booster by applying a predeterminedinput force which shifts the position of the movable wall to abut theoutput member with the stop and bring the movable wall to a testlocation;

d) determining the distance between a reference surface at the boosterhousing and the movable wall at the test location;

e) comparing the distance in step d) to a distance from a referencesurface of the travel sensor to the tip of an actuating element with thetip located at a point located so that the travel sensor signal outputcorresponds to the test location of the movable wall;

f) installing the travel sensor in the booster housing while locatingthe travel sensor reference surface by means of the booster housingreference surface using a suitable spacing means to locate the tip ofthe actuating element at the test location of the movable wall with saidtravel sensor actuating element set in said travel sensor at saidlocation corresponding to said test location.

The spacing means employed can be the selection of a replaceable tipsized to create the appropriate spacing distance.

Another spacing means can be provided by selecting a properly sizedholder installed in the booster housing with the travel sensor assembledinto the holder. The holder can also be adjustable to vary the locationof the installed travel sensor. By these two latter operations anexchange of the travel sensor will be simplified, and the advantageoffered by this approach consists in that in this case, the adjustmentis carried out at the brake power booster whose condition is no longerchanged. In the former approach using replaceable tips, the adjustmentis carried out at the travel sensor, so that it must be carried outagain in the event the travel sensor is replaced.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectional view of a power booster and adiagrammatic representation of a measuring arrangement for carrying outthe inventive process;

FIG. 2 is a partially sectional view of a power booster and travelsensor which has been adjusted in accordance with the invention;

FIG. 3 is an enlarged, fragmentary, and partially sectional view of afirst embodiment of a sensor accommodating element positioning thetravel sensor; and

FIG. 4 is an enlarged, fragmentary, and partially sectional view of asecond embodiment of the sensor accommodating element.

DETAILED DESCRIPTION

FIG. 1 shows a vacuum brake power booster 1 which is to be equipped witha travel sensor, not shown in the drawing, which is connected through anon-return valve 6 to a vacuum source 2. The booster housing 10 issealed to be airtight. A diagrammatically illustrated stop 3 having aportion projecting into the booster housing 10 of defined length Y, isinstalled during the measuring procedure. The stop 3 serves to engage apower output member 9 transmitting the output power of the vacuum brakepower booster 1, with a predetermined input force F exerted on the inputmember of the booster.

Simultaneously, a sensor accommodating element 7 is inserted in anopening 8 being provided in the booster housing 10, the opening 8accommodating installation of the aforementioned travel sensor after theadjustment process is complete.

In the course of the measuring procedure, a measuring instrument 4 isintroduced through the sensor accommodating element 7 and sealed off bymeans of a seal 5. The function of the measuring instrument 4 consistsin determining, at a fixed moment with the movable wall 11 at a testlocation with the input force F applied and the output member 9 againstthe stop 3, the distance A between a travel sensor mounting referencesurface which is defined at the booster housing 10, i.e., between thefront face 12 of the sensor accommodating element 7, on one hand, and amovable wall 11 which exerts the boosting power of the vacuum brakepower booster 1 on the output member 9. The predetermined known inputforce F having been applied to the input member, the movable wall 11 isadvanced so that the power output member 9 is caused to be slid in thedirection of the stop 3 until the power output member 9 abuts againstthe stop 3. As a result, the movable wall 11 comes to be positioned inan advanced test location shown in phantom lines.

The axial distance A between the front face 12 of the sensoraccommodating element 7 and the movable wall 11 corresponding to thatposition is compared to a functional length measure of the travel sensor13 (FIG. 2) to be used whose actuating element 14 interacts with themovable wall 11 during operation. The said functional parameterpreferably corresponds to the distance from a reference surface on thetravel sensor 13 to the tip of the actuating element 14 at the momentwhen a predetermined signal output of the travel sensor 13 is reached,corresponding to the test location of the movable wall 11.

Subsequently, the correct length of a spacing element, for example of aspacing cap 15, is determined on the basis of the result of theforementioned comparison. In order to facilitate the correlation of thespacing caps 15 of different length to the results of the comparison, itis envisaged that a defined color corresponds to each length measure ofthe spacing caps 15, for example red, green, blue or white. Upon theselection of the right spacing cap 15, the latter is plugged onto theend of the actuating element 14 and the travel sensor 13 is introducedinto the sensor accommodating element 7 and secured against sliding bymeans of a retaining ring 16. This completes the adjusting procedure.

FIG. 3 shows a first embodiment of a sensor accommodating element 17which corresponds to a positioning of the travel sensor 13 in respect ofthe movable wall 11 mentioned before and not shown in the drawing, sothat the adjustment is carried out directly at the vacuum brake powerbooster housing 11. For this purpose, for example four groups of sensorholders 17 of different dimensions are furnished one of which isselected depending on the distance between the aforementioned referencesurface and the movable wall 11. In this case, the reference surface isconstituted by the surface of the booster housing 10 which accommodatesthe travel sensor 13. As will be seen in FIG. 3, the sensor holder 17 isprovided projecting into the inner space of the booster housing 10 witha plurality of locking projections 18 which in the mounted condition ofthe sensor holder 17 within the booster housing 10 catch behind the edgeof the opening 8 which is provided for the purpose.

An elastic seal, preferably an O-ring 27, which is positioned betweenthe surface of the booster housing 10 and an annular surface 28 on thesensor holder 17 provide effective sealing of the sensor 17 to thebooster housing 10. In order to fix the travel sensor 13 in the sensorholder 17 upon its mounting, the portion protruding outside the boosterhousing 10 is formed, with a radial peripheral groove 19 whichaccommodates the retaining ring 16 holding the travel sensor 13. Thedistance L between the surface of the booster housing 10 and the flankof the peripheral groove 19 which is positioned nearer to the boosterhousing 10 is the dimension defining the proper holder 17 to achieveproper adjustment of the travel sensor.

The sensor holder 17 may be fixed within the booster housing 10 by othermeans such as, for example by a bayonet catch. For this purpose, thesensor holder 17 is furnished, for example, with a plurality of radialprojections which are inserted into matching clearances in the boosterhousing 10, whereupon the sensor holder 17 is rotated so that theprojections again are engaged behind the edge of the opening 8, the sealwhich seals off the sensor accommodating element furnishing thenecessary prestressing and retaining force for the bayonet locking.

The sensor holder assembly 20 shown in FIG. 4 affords adjustment of itsoverall length to properly locate the tip of the travel sensor 13. It iscomposed of a first part 21 which is passed through the booster housingopening 8 from the inside, and of a second part 22 which is positionedoutside the booster housing 10. The first and second parts 21, 22 arecoupled to each other by means of a threaded union 29.

In the course of mounting of the illustrated sensor accommodatingassembly 20, the first part 21 is plugged through the opening 8 and issecured against falling out by means of a spring ring 23. Afterdetermining the above-mentioned distance "A" between the movable walland the reference surface at the booster housing 10, and upon havingfixed the length "L" which determines the position of the mounted travelsensor 13, the second part 22 is screwed onto the first part 21, thefirst part 21 being rotated with a tool (not shown) engaging withgrooves 25. In the final phase of threaded advance, a nose 24 at the endof the second part 22 facing the first part 21, enters a gap beingprovided in the booster housing 10 adjacent opening 8. The nose 24 afterentering the opening prevents the second part 22 from rotating, toconstitute an antirotation means.

In this design version, the seal 27 which seals the second part 22 tothe booster housing 10 is positioned in an annular groove 26 in thefront side of the second part 22 which faces the booster housing 10. Thegroove flanks are inclined so that the seal 27 cannot fall out of theannular groove 26 in the course of mounting

As soon as the length "L" defined before is reached by threading of part22 on part 21, the adjusting procedure is ended, so that the travelsensor 13 can be inserted and be located and secured by means of theretaining ring 16. In this context, the front face of the first part 21which faces away from the inner space of the booster housing 10 servesas a supporting surface for the seal 5 which seals off the travel sensor13 in respect of the sensor holder assembly 20.

We claim:
 1. A process for the adjustment of a vacuum brake powerbooster having a booster housing, a movable wall in said housing subjecton one side to a vacuum to create an output force, an input member, andoutput member connected to said movable wall, and an associatedelectrical travel sensor for monitoring the position of said movablewall, in which the axial distance between an actuating element of saidtravel sensor and said movable wall is adjusted, characterized by thesteps of:a) mounting a stop having a defined length into said boosterhousing of said vacuum brake power booster so as to be engaged by saidoutput member upon advance of said movable wall; b) applying a vacuum toone side of said movable wall in said booster housing; c) actuating saidvacuum brake power booster by applying a predetermined input force tosaid input member to advance the position of the said movable wall andcause said power output member to abut said stop and locate said movablewall at a test location; d) determining of the distance between areference surface against which the travel sensor is to be mounted andsaid movable wall at said test location; e) comparing the distancedetermined in step d) to the distance between a reference surface onsaid travel sensor and the tip of an actuating element of said travelsensor with said tip positioned in said travel sensor at a locationcorresponding to said test location of said movable wall; f) installingsaid travel sensor against a locating surface fixed with respect to saidbooster housing and spaced to locate said tip of said actuating elementat said test location in said booster housing with said actuatingelement located in said travel sensor at a location corresponding tosaid test location.
 2. The process according to claim 1 wherein in saidinstalling step, said travel sensor is mounted abutting said boosterhousing reference surface, and a replaceable tip element is mounted onsaid actuating element of a dimension so as to locate the outermostsurface of said tip of said actuating element at said test location. 3.The process according to claim 1 wherein in said installing step, aholder of proper dimensions is mounted in said booster housing travelsensor opening, located against a booster housing surface, and saidtravel sensor is mounted in said holder, so as to be accurately locatedaxially with respect to said holder dimensions such as to locate saidtip of said actuating element at said test location.
 4. The processaccording to claim 2 wherein a series of tip elements are constructed ofa range of sizes and a properly sized tip is selected from said seriesto locate said outmost surface of said tips closest to said testlocation.
 5. The process according to claim 4 wherein each of said tipelements in said series is made with a different color to aid in saidselection.
 6. The process according to claim 3 wherein a series ofholders is constructed of a range of sizes and a properly sized holderis selected to locate said tip of said actuating element at said testposition.
 7. The process according to claim 3 wherein each of saidholders in said series is made of a different color.
 8. The processaccording to claim 1 wherein a two piece holder is mounted in a boosterhousing opening, one part located against a surface adjacent saidopening, and adjusting the other part axially with respect to said onepart, and axially locating said travel sensor on said other part.